S8 MORPHOLOGY OF GYMNOSPERMS 



6. Relationship to other gymnosperms 



When Oliver and Scott (39, 48) proposed the name Pteridosper- 

 mae, "to embrace those paleozoic plants with the habit and much 

 of the internal organization of ferns, which were reproduced by means 

 of seeds," it was with the claim, implied in the name, that it represented 

 a third great group of seed plants, coordinate with gymnosperms and 

 angiosperms. Fuller knowledge and a stricter definition of the group 

 was awaited with interest. Later, Scott (58) said that a strict 

 definition was not possible as yet, but that the following provisional 

 one was suggested : " Plants with the habit and certain of the anatomi- 

 cal characters of ferns, bearing on fronds only slightly differentiated 

 from the vegetative foliage seeds of a cycadean type of structure." 

 There seemed to be no sufficient reason for establishing a group 

 coordinate with gymnosperms upon such comparative features; for 

 it certainly possessed the important character of gymnospermy. Still 

 later, Scott (69) formulated his reasons for regarding pteridosperms 

 as worthy of separation from gymnosperms, under two categories: 

 (i) megasporophylls and microsporophylls little modified from 

 ordinary vegetative fronds; (2) anatomical structure more fernlike 

 than in gymnosperms. The cycadophytes as a whole have equally 

 fernlike foliage and sporophylls, and the anatomical peculiarities 

 can nearly all be duplicated among the more primitive gymnosperms. 

 The group is then defined as follows: "Male and female sporophylls 

 little differentiated from the vegetative foliage; no cones formed; 

 anatomy of either stem, or leaf, or both, of a filicinean type, as was 

 also the habit." It is hard to see that such characters are more 

 important than those which distinguish the acknowledged groups of 

 gymnosperms, and of equal importance with those that distinguish 

 gymnosperms from angiosperms. We are compelled to regard 

 pteridosperms as the most primitive known group of gymnosperms, 

 and our reasons for calling them Cycadofilicales have been given 

 above (p. 3). 



There is no more suggestion of the organization of a strobilus, 

 and no more extreme differeotiation of a sporophyli, than among 

 ferns; so that in these respects the group has remained at the fern 

 level. Among living cycadophytes, the megasporophylls of cycads 

 do not always form a comDact strobilus, and every gradation is found 



